Isotope Geochemistry and Geochronology of Syn-Depositional Volcanism in Porongos Metamorphic Complex, Santana Da Boa Vista Antiform, Dom Feliciano Belt, Brazil: Onset of an 800 Ma Continental Arc

Abstract

The Porongos Metamorphic Complex (PMC) is composed of supracrustal rocks, predominantly pelitic micaschist, quartzite and felsic metavolcanic rocks. It represents the remnants of a Neoproterozoic sedimentary basin developed in the western Gondwana, now located in the central section of Dom Feliciano Belt in southern Brazil. Isotope signature comparison and U-Pb ages shows that there are at least three main source-areas for the Porongos sediments: (i) one that can be related to Paleoproterozoic terrains; (ii) a younger component with Mesoproterozoic (1.5-1.2 Ga) ages; and (iii), a Neoproterozoic source with magmatic zircons (0.8 Ga), with relative age distribution mostly between 1.7 and 1.0 Ga, TDM ages between 2.58 and 1.71 Ga, and younger ages of ca. 1.21 Ga, which can be related to 1.4-1.0 African signature sources. Ten concordant analysis obtained in zircon grains from a metarenite rock yield 206 Pb/ 238 U median age of 802 +26/-33 Ma, which is related to metavolcanic samples from PMC and correlates with the Neoproterozoic Cerro Bori Continental Arc, indicating a syn-depositional volcanism in the sedimentary record. The depositional setting for these sequences can be understood as an evolution between a passive margin developed after 1.6 Ga and a terrain-collisional setting (ca. 570 Ma).

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“…Considering the reported 87 Sr/ 86 Sr ratios and U-Pb ages (see 4.3), it's possible to admit this sea would represent the initial rifting phase of the Brazilides Ocean Oyhantçabal et al (2011). Data from Cerro Bory presented by Lenz et al (2012), data from Porongos Metamorphic Complex from Gruber et al (2016) and Gariep Belt samples from Frimmel & Föelling (2004); S&K evolution curve from two stage model's evolution of Stacey & Kramers (1975).…”

Autochthonous origin of the Encruzilhada Block, Dom Feliciano Belt, southern Brazil, based on aerogeophysics, image analysis and PT-paths

“…The foreland Tijucas Fold Belt (Hasui et al, 1975) is a deformed and metamorphosed multi-phase, volcano-sedimentary basin (e.g. Gruber et al, 2016a;Pertille et al, 2015;Höfig et al, 2017). In southernmost Brazil it is composed of two distinct sequences tectonically imbricated due to a westwardvergent thrust (Jost and Bitencourt, 1980;Höfig et al, 2017;Battisti et al, 2018).…”

New insights into the Gondwana breakup at the Southern South America by apatite fission-track analyses

“…1) is composed of metasedimentary rocks intercalated with metavolcanic rocks of the Porongos Complex with ages from ca. 0.5 to 2.8 Ga (Chemale Jr., 2000;Saalmann et al, 2011;Basei et al, 2008;Gruber et al, 2016), granitic-gneissic rocks of the Encantadas Complex. The Encantadas Complex is interpreted as a Paleoproterozoic active continental arc (Saalmann et al, 2011;Philipp et al, 2008) and granitic intrusions and sedimentary rocks.…”

“…The Nico Pérez Terrane (Bossi and Campal, 1992), located East of the Sarandí del Yí Shear Zone (Fig. 1), composed of Lopes, 2009;Chemale Jr. et al, 2012;de Oliveira et al, 2016;and Gruber et al, 2016).…”